System for dewatering a flowline including a multiphase pump connected at a lower end of the flowline

Patent metadata

Field	Value
Publication number	US-12098796-B2
Application number	US-202217574246-A
Country	US
Kind code	B2
Filing date	Jan 12, 2022
Priority date	Jul 2, 2020
Publication date	Sep 24, 2024
Grant date	Sep 24, 2024

Abstract

A system for dewatering a subsea gas pipeline includes a pig launcher at the pipeline's upper end, which may be at or near the sea surface, and a pig receiver at the pipeline's lower end, which may be at or near the sea floor. A multiphase pump unit is deployed at the pipeline lower end and is configured to provide sea water suction to aid in a pig train being forced downwards through pipeline. The multiphase pump is configured to handle some amount of gas leaking around the pig train. A choke system may allow sea water to enter the flowline, thereby lowering the gas volume fraction (GVF) and preventing the GVF from exceeding the ability of the multiphase pump. For deeper water applications, a second pump may be provided in series that may be a single pump if positioned downstream of the multiphase pump.

First claim

What is claimed is:

1. A subsea fluid flowline dewatering system, comprising:
at least one multiphase pump positioned at a lower end of a fluid flowline to be dewatered;
a multiphase flowmeter in communication with the fluid flowline and positioned on a suction side of the at least one multiphase pump;
a choke valve in fluid communication with the fluid flowline and positioned on the suction side of the at least one multiphase pump, the choke valve being selectively operated to allow seawater from an exterior of the fluid flowline to flow into the suction side of the at least one multiphase pump in response to a gas volume fraction (GVF) estimated by the multiphase flowmeter; and
a pig train configured to be introduced at an upper end of the fluid flowline, the at least one multiphase pump being configured to provide suction at the lower end of the fluid flowline, thereby supporting downward travel of the pig train towards the lower end of the fluid flowline.

2. The flowline dewatering system of claim 1 , wherein the fluid flowline is a gas flowline.

3. The flowline dewatering system of claim 1 , wherein the at least one multiphase pump is configured to process fluids at least 10% GVF, wherein the choke valve is operated to allow seawater to flow into the suction side of the at least one multiphase pump when the GVF estimated by the multiphase flowmeter exceeds 10% GVF.

4. The flowline dewatering system of claim 1 , wherein the at least one multiphase pump is configured to process fluids at least 30% GVF.

5. The flowline dewatering system of claim 1 , further comprising a flow mixer unit positioned upstream of the at least one multiphase flowmeter, the flow mixer unit configured to mix gas and liquid to facilitate GVF estimations by the at least one multiphase flowmeter.

6. The flowline dewatering system of claim 1 , wherein the lower end of the fluid flowline is disposed less than about 1500 meters below the upper end.

7. The flowline dewatering system of claim 1 , further comprising a second pump positioned in series with the at least one multiphase pump.

8. The flowline dewatering system of claim 7 , wherein the second pump is a single phase pump configured to process fluids less than about 10% GVF.

9. The flowline dewatering system of claim 8 , wherein the lower end of the fluid flowline is disposed greater than about 1500 meters below the upper end.

10. The flowline dewatering system of claim 1 , wherein the choke valve is operated to allow seawater to flow into the suction side of the at least one multiphase pump when the GVF estimated by the multiphase flowmeter exceeds 10% GVF.

11. The flowline dewatering system of claim 1 , wherein the choke valve is operated to allow seawater to flow into the suction side of the at least one multiphase pump when the GVF estimated by the multiphase flowmeter exceeds 30% GVF.

12. A method to dewater a subsea fluid flowline having an upper end and a lower end, the method comprising:
launching a pig train at the upper end;
pumping a fluid in the subsea fluid flowline out of the subsea fluid flowline with a multiphase pump positioned at the lower end, thereby supporting downward travel of the pig train towards the lower end; and
operating a choke valve to allow seawater from an exterior of the fluid flowline to flow into a suction side of the multiphase pump based on a gas volume fraction (GVF) of the fluid in the fluid flowline detected by a multiphase flowmeter.

13. The method of claim 12 , wherein the subsea fluid flowline is a gas flowline.

14. The method of claim 12 , wherein the subsea fluid flowline extends from shore to subsea.

15. The method of claim 12 , wherein the multiphase pump is configured to process fluids at least 30% GVF.

16. The method of claim 12 , further comprising mixing gas and liquid phases of the fluid in the subsea fluid flowline to facilitate adequate GVF estimations by the multiphase flowmeter.

17. The method of claim 12 , wherein the lower end of the subsea fluid flowline is less than about 1500 meters below the upper end.

18. The method of claim 12 , further comprising pumping the fluid with a single phase pump positioned in series and downstream of the multiphase pump.

19. The method of claim 18 , wherein the single phase pump configured to process fluids less than about 10% GVF, wherein the choke valve is operated to allow seawater to flow into the suction side of the multiphase pump when the GVF estimated by the multiphase flowmeter exceeds 10% GVF.

Assignees

• Onesubsea Ip Uk Ltd

Inventors

• Kjellnes Hans Fredrik
• Ekeberg Ina
• Marthinussen Svein-Arne
• Dale Helge
• Klepsvik Knut
• Helmers Per Bloch

Classifications

• F04D31/00 Primary

  Pumping liquids and elastic fluids at the same time · CPC title

• F04D25/0686

  specially adapted for submerged use · CPC title

• F04D13/086

  the pump and drive motor are both submerged · CPC title

• F17D1/005

  for a two-phase gas-liquid flow · CPC title

• E21B41/0007

  for underwater installations (E21B41/005, E21B41/04, E21B41/06, E21B41/08, E21B41/10 take precedence) · CPC title